You know I was looking at my hood today without the inserts on it and the openings are really quite large. The inserts make that opening not even half of what they are when the inserts are out. I wonder how hard it would be to have the insert outside dimensions with the opening larger and a black screen in there. I think it would really pull in a decent amount of fresh air. The 68 RR scoop has a lot larger opening so it would be worth more hp I would think. I would want something like a regular airbox, similar to the fresh air hoods like that 68-69 RR or 70 air grabber box. That kind of setup would seem to be a whole lot of trouble for minimal gains though.

I don't have access to the aerodynamic analysis people I used to work with. Joe H. could give you an exact answer as to the height of the boundary layer for our R/T hood example, temperature and pressure compensated.But we know this, the boundary layer grows in height with distance from the "leading edge". ON a typical jet fighter, F-15, F-18 or the FB-111 the engine inlets are offset from the fuselage by about 6 inches roughly. So the boundary layer was less than 6 inches tall after traveling about 20 feet at any Mach speed.Now think about a Challenger R/T hood. The scoops are what, maybe 3 feet back from the leading edge, and our speed is a bunch less than Mach 1. I'm going to guess the boundary layer at the scoop entrance would be a few tenths of an inch tall if it were lucky; meaning nearly all of the air entering the scoops would be flowing true airspeed of the vehicle. Remember the air flowing directly against the hood is not moving at all. And as you say, the air is COLD, not engine heated.I will suggest the trans am hood would be perfectly functional, no boundary layer ingestion what so ever. JMO based on some experience with aircraft airflow.

sleepychallenger

good info. i think i am going to build an air box for my 6 pk hood. would be cool to see the rally hood with a fresh air system hooked from the twin snorkle air cleaner to the scoops. the sucking of the engine should change the way the air is flowing too right?

Something like this from a Buick GS could be Mickey rigged I would imagine. The foam insulation is tall so it would give lots of area for the foam to conform to the irregualr under surface of the hood/scoop area. You may need to take off the portion of the scoop that serves as a drip rail.

It would be completely sealed so the only place air can be sucked in is from the scoops=cool air unless the ambient air is hotter than the under hood air which is unlikely, unless you're in Arizona somewhere in the summer.

Logged

1972 Dodge Challenger Rallye 340, AT, Code TB3=Super Blue, SBD=8/17/1971. Yes, a Rallye without the fender louvers from the factory because of the body side molding option.

the sucking of the engine should change the way the air is flowing too right?

The engine would create a low pressure, which would promote more airflow thru the scoops. ON the SR-71 aircraft, at Mach 3 the engines pulled in so much air there was actually a vacuum in front of a large portion of the plane, so it went even faster.Here's a boundary layer test: Tape pieces of knitting yarn on the hood in front of the scoops, with some yarn under one end of the tape, and several inches of free length sticking out beyond the tape. Lay the free ends pointing across the hood, IE not pointing at the scoops. Now drive the car at only 30 mph. Were the free ends drawn into the scoops?? IF yes, then the boundary layer was "thinnner" than the thickness of the yarn. If NO, then try it again at 50 mph. The yarn should surely be drawn into the scoops.We need a little pressure manometer, or wind speed indicator to measure the velocity of the air entering the scoops. If there was an air cleaner box, the manometer would tell us the increase in pressure over atmospheric inside the box. The pressure increase combined with the "low" pressure created by the engine vaccum would improve performance.Note that the Super Stock hoods on the early Cuda's and Dart's had very large air inlets. So really a large inlet is needed to make most use of the "ram" effect at low airspeeds (around 100 mph).I'll try the knitting yarn test when I get my Challenger up and running. Might be next year though.

So SS scoop has over 10 times the required area to be "super" effective at ramming air into carbs at high speed.Notice even the dual snorkel air inlet is lacking enough area to really work. The old trick of turning the air cleaner lid over opens the air filter to much more flow area than a dual scoop can provide.Also notice the R/T dual scoops actually provide the most air over any stock snorkel type air cleaner. So should be a benefit.Need to do the yarn test for R/T scoop effectiveness. They use it on airplanes in the wind tunnels.Like your all saying, we need a good box that seals the air cleaner base to the underside of the hood.What should be done for rain water draining??? Maybe back corners of the box would have "low" points built in with small holes drilled to let water out, but not let too much air out.

I'm waiting for rocker arms to show up, so worked on R/T hood scoops today. Stock scoops have total area (2 scoops) of 10.4 sq.inches. Ported, they have 14.8 sq.inches. Thats a 42% increase in available area.Now compare to TQ 850 cfm carb: Ported scoops have 14.8-11.5=3.3 sq.inch area more than carb throttle plates. Thats 29% more area than plates. Unported scoops had 10% less area than throttle plates.The ported scoop is below unported in photo, and I only worked the lower lip as shown in photo,

On a Vehicle, with a blunt nose, the air comes off at a much different angle then then one off a jet, which is made to cut through the air at the best of its ability. The Challenger, Cuda, etc... don't have that design, the air flow that moves at the speed of the vehicle is much more then a few inches above the hood. Even with the low pressure that the engine creates, it isn't being forced or pulled into the engine with any effiency to increase horsepower then a normal open element air cleaner can do.

Here you can see the basic way the air is flowing over a car with even a little bit of design work to cut through the air, with the Challenger, Charger, Cuda's blunt nose, it is even worse.

Thats what I have been trying to get at. It really does not matter how much ram effect the scoops have because they will still be drawing all the cool air they need from outside the engine bay. That in itself I know is worth some horsepower gains. Its not like it would rob horsepower because of the slow moving boundary air.